1. Field of the Invention
The present invention relates to an optical lens having a lens surface on each surface and a method of manufacturing the same, and more specifically, to an optical lens that is injection-molded by a mold and that has a convex portion or a concave portion in the center of both lens surfaces and a method of manufacturing the same.
2. Description of the Related Art
As a method of manufacturing an optical lens such as a photographing lens of a camera or an imaging lens of an optical element, an injection-molding method is generally used, which is suitable for mass production at a low cost. In the injection-molding method, upper and lower molds which are formed to correspond to the contour of a desired molded product are arranged to be opposed to each other, a molten material is injected into the space between the upper and lower molds to be cooled and solidified, and then a molding product is formed.
In addition, in order to image an object by use of the formed optical lens, a plurality of optical lens are generally arranged in the direction of the optical axis to constitute a lens system. Since the deviation between the central axes of the respective lenses becomes a cause of reduction in resolution, it is necessary that the respective lenses constituting the lens system should be arranged with high precision. The deviation between the central axes of the lenses can be adjusted by a piezoelectric element which is arranged in each of the lenses to be moved minutely. As such an adjusting method, for example, there is provided a method exemplified in Japanese Unexamined Patent Application Publication No. 2002-277705.
However, in the above-described adjusting method in which an optical lens having a lens shape on each side is used, there is no countermeasure against the case where both lens surfaces are deviated with respect to the central axis to be eccentric with each other due to an arrangement error of the upper and lower molds when the optical lens is molded. In the case of the eccentricity of a single lens, the eccentricity amount of both lens surfaces is measured, and based on the measurement result, the positions of the molds are adjusted. However, in the conventional method of measuring the eccentricity of a single lens, the center of the lens surface is calculated from the contour of the lens and the height of the lens, respectively, and then, the deviation between the centers of both surfaces is measured, which means that the measurement becomes complicated because a three-dimensional measuring machine needs to be used.
In addition, as digital cameras are recently miniaturized and have high resolution, lenses are also required to be miniaturized and have high resolution. Further, a permissible value of an eccentricity amount of a single lens is less than several micrometers. The difference between the virtual center calculated by the above-described method and the actual optical center easily occurs. In particular, in the case of an injection-molded optical lens, the contour of the lens is easily distorted due to the flow of injected resin, so that an eccentricity amount is hardly measured and adjusted with high precision.